Severe developmental delays, cognitive impairment and encephalopathy (which for consistency are referred to as HIV-associated Neurocognitive Disorders [HAND]) occurred in 30-50% of perinatally infected children prior to the availability of effective combination antiretroviral therapy (ART). While with ART the incidence of encephalopathy has been reduced, severe cognitive impairment is still identified in 15-20% of HIV-infected children. Additionally, although much research has been performed on HAND, the neuropathogenesis of CNS impairment remains to be elucidated. The research proposed will apply state-of-the-art exome sequencing technology to identify the host genetic factors associated with HAND in children. The specific aims of this proposal are: Aim 1: Apply whole exome sequencing (WES) to identify novel candidate genetic variants associated with HAND in a discovery cohort of perinatally infected children. In this aim, WES will be used to identify novel genetic locus variants and pathways that are associated with HAND in children. The hypothesis to be tested is that by examining all protein-coding sequences (exomes) in addition to HLA and killer Ig-like receptor (KIR) alleles in 500 HIV-infected children equally divided between subjects with HAND and those with normal neurocognitive and neurodevelopmental function gene locus variants will be identified which are associated with CNS disease. Aim 2: Evaluate the associations of the genetic variants with CNS disease in replication cohorts of HIV-infected children in the U.S. Having identified novel genetic variants that are associated with HAND in Aim 1, the association of ~500 variants and specific HLA/KIR genotypes of highest significance in the discovery cohort will be tested for association in two U.S. replication cohorts with similar ethnic and socioeconomic backgrounds as the discovery cohort. Targeted exome sequencing and genotyping of specific HLA and KIR SNPs will be performed. Aim 3: Examine the genetic variants identified in Aims 1 and 2 associated with CNS disease of children in the U.S. for association of these polymorphisms with CNS disease in a cohort of HIV-infected children in South Africa. The hypothesis to be tested is that although a cohort of children born in South Africa differs significantly from those born in the U.S., genes carrying variants identified to alter the risk of HIV-related CNS disease in U.S. born children will also be important determinants of risk for children from South Africa. For these studies, targeted exome sequencing and specific HLA and KIR genotypes will be applied to South African HIV-infected children who have undergone extensive neuropsychometric and developmental testing. To our knowledge, our research has access to the largest cohorts of well-characterized HIV-infected children with CNS outcomes in the world, and will for the first time apply exome sequencing to large number of HIV-infected children. The findings of this research will provide insights into the pathogenesis of HAND and suggest novel strategies how to treat and to prevent the CNS disease associated with HIV.